THE INTEGUMENTARY APPENDAGES. 



793 



The derma is not of the same thickness everywhere, being much thinner 

 where it is protected from external injury, as on the under- surf ace of the 

 belly, the inner side of the legs, thighs, etc. ; it is also thin around the 

 margin of the natural openings, to permit the transition between the two 

 membranes, and endow these apertures with their necessary dilatabiiity. 



Fig. 363. 



SECTION OF HORSE'S SKIN; FROM WING OF THE NOSTRIL. 



E, Epidermis ; D, Derma ; 1, Horny layer of the epidermis ; 42, Rete mucosum ; 3, 

 Papillary layer of the derma ; 4, Excretory duct of a sudoriparous gland ; 5, 

 Glomerule of a sudoriparous gland ; 6, Hair follicle ; 7, Sebaceous gland ; 8, 

 Internal sheath of the hair follicle 9, Bulb of the hair r 10, Mass of adipose 

 tissue. 



STRUCTURE. The derma is composed of fasciculi of conjunctival tissue 

 interwoven and matted in a solid manner, and in the meshes of which are some 

 smooth muscular fibres, which, by their contraction, produce the condition of 

 the skin known as the cutis anserina (goose-skin). Somewhat loosely woven in 

 its deepest part to form the reticular layer (or corium), the derma contains 

 the roots of the pilous follicles, the sudoriparous (or sweat) glands, and small 

 masses of adipose tissue ; superficially, its structure is very condensed, to 

 constitute the papillary layer, whose uppermost 

 limit forms an amorphous border. 



The papillce are of two kinds vascular 

 and nervous, and are regularly arranged in 

 parallel series : they are most numerous in 

 those parts of the skin specially destined for 

 the exercise of touch, as at the lips, in the 

 keratogenous membrane (of the foot), and 

 other parts where sensibility is very acute 

 such as the scrotum, sheath, and integuments 

 of the penis. The papillary prolongations of 

 the derma are conical or fungifonn, and pedi- 

 culated ; their dimensions are very variable ; 

 measuring from T f^th to ^th of an inch in length, and from -^th to 



Fig. 364. 



